This invention relates generally to an apparatus having a transducer or transducers for data transfer with a rotating data storage disk such as a flexible magnetic disk having a multiplicity of concentric annular record tracks on one or both of its major surfaces. More specifically, the invention pertains to a system in such rotating disk data storage apparatus for the constant current driving of a stepper motor for transporting the data transducer or transducers from track to track on the disk, in the face of possible fluctuations in supply voltage.
The flexible magnetic disk apparatus, or floppy disk drive according to common parlance, is usually not self contained; it is subservient to a host system as in such familiar electronic data processing systems as personal computers and word processors. Usually, therefore, disk drives have no power supply of their own but are powered from the host system. The power supply circuit of the host system is provided with a voltage regulating circuit such as a switching regulator. Since a number of loads are connected to the voltage regulating circuit, the supply voltage fed to each load is not necessarily constant even if the output voltage itself of the regulating circuit is constant.
One of such load is the bidirectional stepper motor which is customarily employed for transducer positioning, as disclosed for example in U.S. Pat. No. 4,677,359 to Enami et al. Conventionally, the stepper motor suffered from irregularities in supply voltage. Fluctuations in the voltage supplied to the stepper motor were particularly objectionable because the transducer or transducers would travel different distances depending upon the direction of rotation of the stepper motor in response to such fluctuating supply voltage. Excessively high drive voltages for the stepper motor were also undesirable because of much noise produced during track seek operations and of waste of energy.
It might be contemplated to provide a known voltage regulating circuit exclusively for the stepper motor. This solution is unsatisfactory as the additional voltage regulating circuit of conventional design would add substantially to the cost of the disk drive.